This invention relates generally to digitally tuned television receivers and specifically to such receivers that incorporate memories for storing channel-related receiver adjustment information.
Memory saving is achieved with the invention by providing full receiver-adjustment data memory capability for only a limited number of channels, though the receiver can receive any televised channel signal, albeit without elaborate picture corrections. The television receiver is sequentially tunable to any channel by operation of a simple up/down switch or directly tunable via the input of a two digit channel number. The limited location adjustment data memory may provide storage of channel-related information such as fine tuning, color level, tint, antenna orientation, multipath signal correction, etc. In short, for a limited number of channels, the receiver may be individually programmed to a very high degree of sophistication.
There are a number of well-known all-channel television tuning systems. In U.S. Pat. No. 3,961,266, issued June 1, 1976 to the inventor, a system of sampling the oscillator to determine its frequency for providing direct tuning within a restricted freqency window by channel number is disclosed. The system also discloses a sixteen position (16.times.8 bits) programmable channel number memory for retention of the channel numbers of up to fifteen often-viewed television channels in any viewer-determined sequence. One position of the memory, which is unavailable for programming, is accessed whenever a channel number is directly entered into the system. The other programmed memory positions are sequentially accessed by clocking a memory address counter up or down. Unprogrammed memory positions are skipped in the "operate" mode. The system provides the viewer with the option of scanning among only pre-programmed television channels rather than being limited to selection of channels by input of two digit channel numbers.
In U.S. Pat. No. 4,023,107, dated May 10, 1977 and issued to the inventor, tuning is accomplished by channel numbers generated by a viewer-controlled channel number counter. The channel number display is observed until the desired channel number is produced. (The receiver instantly and automatically tunes to the television signal corresponding to the generated channel number.) The viewer may by operation of a skip/stop switch in the Program mode, store a stop signal in an 82.times.1 channel number addressed memory. Thereafter in the Operate mode, in response to an up/down switch, the channel number counters are clocked at high speed between programmed (selected) channel numbers.
The prior art also includes a variety of all-channel television receivers having a limited number of tuning positions, which are usually vertically oriented adjacent to the picture tube. Each position may be programmed to receive any of the 82 FCC allocated television channels by sequencing through the various positions and tuning in a desired channel at each position. Translucent channel number identification tabs corresponding to the number of the tuned channel are generally inserted adjacent to the tuning position. The receiver may be thereafter tuned either remotely or via an up/down switch. Some receivers incorporate push buttons at each tuning position and direct tuning to a programmed channel may be accomplished by pushing the appropriate button.
Each of these systems incorporates a memory having fewer locations than there are FCC allocated television channels. This represents a practical solution since only a very few of the 82 allocated channels are available in any given geographical area. Thus to provide memory of all 82 channels would not only prove cumbersome, but economically wasteful.
Memory costs are a function of memory size or capacity. Therefore, the larger the memory, whether in terms of number of words (locations) or length of words (bits), the greater the cost. The system of above-mentioned U.S. Pat. No. 3,961,266 includes a 16.times.8 memory to provide operational flexibility for the viewer, namely limited channel scanning in addition to direct channel selection by channel number. In the system of the above U.S. Pat. No. 4,023,107, direct access via channel number was omitted in favor of all-channel sequential operation with a simple 82.times.1 skip/stop memory. The other mentioned prior art systems incorporate memories in the form of potentiometers. There have also been all-channel systems which use digital to analog converters for storing tuning words of considerable length. The number of bits of information in memory greatly increases the system cost and complexity. As the trend toward providing even more tuning data to optimize viewing continues, the problem of memory size becomes of critical importance.
In accordance with the invention, significant memory capacity (to enable exceptional control of the displayed image) may be provided for a limited number of channels in an all-channel receiver without incurring enormous cost. In effect, the viewer is enabled to program his receiver with a lot of channel-related tuning information for any of a limited number of television channels while still retaining all-channel tuning capability by channel number. Further, the viewer is also not normally aware of any limitations in his receiver system since all channels are receivable at nominal settings.
To elaborate, viewer advantages are dramatic since at all times he may readily receive any desired channel on his receiver merely by entry of a desired channel number or operation of the up/down switch until the desired channel number appears in the display area. If the entered channel number is not one of those programmed in the limited position memory, the receiver is nominally tuned to the frequency corresponding to that channel number. In most cases an acceptable picture will result because the receiver fine tuning, color, tint, etc. controls are established in the factory at nominal settings. If the selected channel number corresponds to one that has been programmed into the limited position memory, the corresponding receiver adjustment information is read out and appropriate control signals developed in accordance therewith. The system automatically searches for the entered channel number among the limited locations of the memory. Thus for desired channels and often-viewed channels, very elaborate receiver adjustment information may be put into the memory and automatically read out to adjust the receiver controls for optimum viewing whenever the channel is selected. Indeed, corrective information regarding antenna orientation and "ghost signals" may be incorporated to produce a truly ideal picture. To provide capacity for such information for every channel would be prohibitive because of the enormous memory required. With the system of the invention only a relatively small limited location, memory need be utilized for selected channels.